Kobayashi, nicknamed as Mr. K (Kobasen in the Japanese versions), is a teacher at Hinokuni Junior High School. Mr. K is also a King of the Celestial World Candidate who gives Ueki his power. He is Ueki's homeroom teacher and had been carefully studying him in order to judge his worth for the tournament.

Kobayashi is usually a laid-back, forgetful, and friendly man, although he can be quite serious, depending on the situation. He has a very strong sense of justice, actually inspiring Ueki long ago when he saved him from falling off a building, and acts as both his mentor and role model.

He is sent to Hell for saving (and thus helping) Ueki in his first fight against Robert Haydn. He then become Mori's god candidate.